Point D is a turning point so the velocity at point D is zero. You indicated that the acceleration at point D is also zero.� An object with zero acceleration either sits at rest for a period of time or is moving with constant speed in a straight line.� A zero acceleration also indicates that the velocity is not changing.� Is the velocity of the ball zero for more than one instant?� When the ball is near point D, is the velocity of the ball ever constant?�

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